Method for transmitting feedback information via a spatial rank index (sri) channel

ABSTRACT

A method for transmitting feedback information via a Spatial Rank Index (SRI) channel includes determining, at an access terminal, a value of a spatial rank index and transmitting, from the access terminal through the SRI channel, feedback information indicating the determined value of the spatial rank index according to a prescribed coding. The codeword of the prescribed coding is one of: (0,0,0,0,0,0,0,0), (1,0,1,0,1,1,0,1), (0,1,1,1,0,0,1,1), or (1,1,0,1,1,1,1,0).

CROSS-REFERENCE TO RELATED APPLICATIONS

Pursuant to 35 U.S.C. §119(e), this application claims benefit ofpriority from U.S. Provisional Application Ser. No. 61/231,986, filed onAug. 6, 2009, the contents of which are incorporated by reference hereinin their entirety.

FIELD OF THE INVENTION

The present invention generally relates to wireless communications, andin particular, to transmitting feedback information in a wirelesscommunications channel.

DESCRIPTION OF THE RELATED ART

In the field of error correction coding, a binary error correction codemay be notated as an [n, k, d] code, where the value ‘n’ represents thelength (in bits) of each codeword of the code, the value ‘k’ representsthe number of information bits encoded in each codeword, and the value‘d’ represents a minimum distance between the codewords. Because the [n,k, d] code is a binary code, the code has a total of 2^(k) codewords. Asa form of shorthand, the binary error correction code may be referred toas an [n, k] code.

The distance between two selected codewords corresponds to the number ofbits (or bit positions) having bit values that are different from eachother. If the distance between two codewords is equal to or greater than(2a+1), where ‘a’ is an integer, then, between the two codewords, up to‘a’ bit errors can be corrected. For example, if two given codewords ofa code are ‘101011’ and ‘110010’, the distance between the two codewordsis 3 because the second, third and sixth bit positions (counting fromthe most significant bit located at the left end) have bit values thatare different from each other. Because the distance is equal to 3, up toone bit error can be corrected.

A minimum value among distances between codewords of a code is referredto as a minimum distance of the code. The minimum distance is a typicalmetric that may be used to evaluate the performance of a code. Thelarger the minimum distance, the less likely that a given codeword willbe erroneously interpreted as another codeword. As such, a largerminimum distance generally corresponds to a higher level of performance.The degree to which a code provides maximization of the minimum distancemay serve as a measure of high performance.

SUMMARY OF THE DISCLOSURE

In accordance with an embodiment, a method for transmitting feedbackinformation via a Spatial Rank Index (SRI) channel includes determining,at an access terminal, a value of a spatial rank index and transmitting,from the access terminal through the SRI channel, feedback informationindicating the determined value of the spatial rank index according to aprescribed coding. The codeword of the prescribed coding is one of:

(0,0,0,0,0,0,0,0),

(1,0,1,0,1,1,0,1),

(0,1,1,1,0,0,1,1), or

(1,1,0,1,1,1,1,0).

In accordance with another embodiment, a method forgenerating/transmitting a codeword includes determining, at an accessterminal, information regarding a value of a spatial rank andgenerating, at the access terminal, the codeword to represent thedetermined information, the generating comprising combining a firstcodeword of a (3, 2) simplex code and a second codeword of a (5, 2)shortened Hamming code.

Another embodiment relates to an access terminal for transmittingfeedback information via a Spatial Rank Index (SRI) channel. The accessterminal includes a controller configured to determine a value of aspatial rank index; and a transmitter configured to transmit feedbackinformation via the SRI channel, wherein the feedback informationindicates the determined value of the spatial rank index according to aprescribed coding. The codeword of the prescribed coding is one of:

(0,0,0,0,0,0,0,0),

(1,0,1,0,1,1,0,1),

(0,1,1,1,0,0,1,1), or

(1,1,0,1,1,1,1,0).

These and other embodiments will also become readily apparent to thoseskilled in the art from the following detailed description of theembodiments having reference to the attached figures, the presentdisclosure not being limited to any particular embodiment disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects and features of the present disclosure willbecome more apparent upon consideration of the following description ofembodiments, taken in conjunction with the accompanying drawing figures.

FIG. 1 is a partial block diagram of various operations implemented by amobile station (MS) transmitter in a MIMO system.

FIG. 2 is a partial block diagram of various operations implemented byan MS transmitter in a MIMO system according to one embodiment.

FIG. 3 shows a flowchart for transmitting feedback information via aSpatial Rank Index (SRI) channel, according to one embodiment.

FIG. 4 is a block diagram showing in more detail various componentswhich may be implemented in a mobile station according to variousembodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following detailed description, reference is made to theaccompanying drawing figures which form a part hereof, and which show byway of illustration specific embodiments of the invention. It is to beunderstood by those of ordinary skill in this technological field thatother embodiments may be utilized, and structural, electrical, as wellas procedural changes may be made without departing from the scope ofthe present invention. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or similarparts.

Various embodiments will be presented herein in the context of awireless communication network and associated entities configured inaccordance with the High Rate Packet Data (HRPD) protocol, which isoptimized for high speed, high capacity data transmissions. However,alternatives to such implementations are envisioned, and teachings withregard to the HRPD protocol are generally applicable to other standardsand air interfaces as well. Moreover, the use of certain terms todescribe various embodiments should not limit such embodiments to acertain type of wireless communication system, such as HRPD. Variousembodiments are also applicable to other wireless communication systemsusing different air interfaces and/or physical layers including, forexample, frequency division multiple access (FDMA), time divisionmultiple access (TDMA), code division multiple access (CDMA), widebandCDMA (W-CDMA), universal mobile telecommunications system (UMTS), thelong term evolution (LTE) of the UMTS, and the global system for mobilecommunications (GSM). By way of non-limiting example only, furtherdescription will relate to an HRPD communication system, but suchteachings apply equally to other system types.

Furthermore, particular embodiments of the invention are directed toproviding an error correction coding scheme to convey spatial rankinformation in an HRPD system (e.g., a system configured in accordancewith HRPD revision C).

The HRPD protocol applies Code Division Multiple Access (CDMA)technology and Time Division Multiplexing (TDM) technology in, forexample, the transmission of data from a mobile station. Due to itsimproved data transmission rate and capacity, an HRPD system can providemultimedia contents in various technical fields of application, such aswireless Internet access, real-time road traffic information, wirelesslive broadcasts, movies, and games.

In Revision C of the HRPD protocol, a MIMO (Multiple Input MultipleOutput) scheme is included. In general, MIMO may involve the use ofmultiple antennas at both the transmitter and the receiver. As such,MIMO may be used to increase a diversity gain in order to reduceperformance deterioration caused by a fading environment of a channel.In addition, MIMO may involve the transmission of multiple layers ormultiple streams. As such, MIMO may be used to increase a data transferrate of a given channel. Relative to a single-input single-output systemusing a single transmitting/receiving antenna, a MIMO system cantransmit a larger quantity of data without requiring an increase infrequency bandwidth.

In a MIMO system, a channel can be decomposed into multiple independentchannels. For example, when the number of transmission antennas is Ntand the number of receiving antennas is Nr, the maximized number ofindependent channels, Ni, equals the smaller of Nt and Nr. Eachindependent channel can be referred to as a spatial layer.

The number of spatial streams that can be multiplexed may be expressedin a MIMO channel matrix, and a rank may be defined as the number ofnon-zero eigenvalues in such a MIMO channel matrix. The rank may also bedefined as the number of independent channels. For example, if the rankof a system equals one, then one spatial stream can be transmitted onone spatial layer. If the rank is two, then two independent streams canbe simultaneously transmitted on two spatial layers. If the rank is K,then K independent streams (e.g., K streams that may have differentrates) can be transmitted on K spatial layers.

In order to obtain gain for multiple antennas, channel-dependentfeedback provided by a user equipment may be used to tune a multipleantenna transmission scheme.

So that MIMO is operated smoothly, channel state information should beavailable at the transmit side (e.g., at a base station). Since suchchannel state information could be measured only at the receiver side(e.g., at the mobile station), this channel state information should befed back to the transmitter from the receiver. The channel stateinformation can be delivered in various ways. For example, theinformation may be fed back via a direct channel quantization. If such adirect channel feedback enables the transmitter to know the channelperfectly, then the transmitter could determine the transmission modeaccording to the channel status.

As another example, the information may be fed back using a transmissionmode related scheme such as an MCS (Modulation Coding Scheme), rank, andprecoding matrix. If the transmitter is provided with an MCS, rank andprecoding matrix that is fed back without error, then the fed back MCS,rank and precoding matrix can be used directly after the reportinginformation is received at the transmitter.

Therefore a reporting of an MCS, rank and precoding matrix may serve asan efficient vehicle for providing channel feedback.

In HRPD revision C, channels have been introduced to deliverMIMO-related feedback such as rank and precoding index. For example, theSpatial Rank Channel (SRC) is used to provide a rank feedback, and theSpatial Signature Channel (SSC) is used to provide a precoding index.

It should be noted that precoding may also be referred to as spatialsignature, precoding, prefiltering, etc. Also, MCS is common to bothnon-MIMO (or single-input-single-output (SISO)) systems up to HRPDrevision B and MIMO systems in HRPD revision C, and MCS can be deliveredvia an existing Direct Rate Control (DRC) channel without anysignificant changes.

With reference to FIG. 1, various operations that may be implemented ina transmitting entity, such as a mobile station (MS) transmitter, in aMIMO system are configured to encode and modulate information includingspatial rank and spatial signature. In the following descriptionregarding FIG. 1, the spatial rank and spatial signature informationwill be described with reference to a system employing 4 transmitantennas. It is understood that, in a system employing only 2 transmitantennas, certain parameters may differ from the 4-transmit-antennasystem. For example, relative to a system employing 4 transmit antennas,a system employing only 2 transmit antennas may require a differentnumber of bits to convey spatial rank and spatial signature information.

With reference to FIG. 1, a transmitter of a mobile terminal isconfigured to encode and modulate a four-bit spatial signature and atwo-bit spatial rank for a system employing four transmit antennas. Thetransmitter includes an In-Phase branch (I-Branch) 10 and a QuadratureBranch (Q-Branch) 15. The I-Branch 10 includes a Bi-Orthogonal Encoder101, a Codeword Walsh Cover (W₀ ²) component 102, a Signal Point Mapper103, a spatial signature channel (SSC) Gain element 104, a Repeater (×8)105, and a Modulator 106. The Q-Branch 15 includes a Bi-OrthogonalEncoder 151, a Codeword Walsh Cover (W₀ ²) component 152, a Signal PointMapper 153, a direct rate control (DRC) Channel Gain element 154,Modulators 155 and 156, and a Walsh Cover (W_(i) ⁸) component 157. Inaddition, the Q-Branch 15 includes a Repeater (×4) 158, a Codeword WalshCover (W₁ ²) component 159, a Signal Point Mapper 160, a spatial rankchannel (SRC) Gain element 161, a Repeater (×8) 162, and an adder 163.

With continued reference to FIG. 1, a four-bit SSC symbol is input tothe I-Branch 10. A two-bit SRC symbol and a four-bit DRC symbol areinput to the Q-Branch 15. Because the SRC symbol is two bits long, thesymbol can convey up to 4 distinct spatial rank values (e.g., spatialrank values ranging from 0 to 3, ranging from 1 to 4, etc.). Similarly,because the SSC symbol is four bits long, it can support up to sixteendistinct spatial signatures. These spatial signatures may be predefinedfor the system, predefined for each particular sector, or negotiatedduring connection setup. According to various embodiments, a set ofdistinct spatial signatures numbering from 9 to 15 are predefined ornegotiated.

As previously described, the two-bit SRC symbol is input to the Q-Branch15. In more detail, the two-bit SRC symbol is input to the Repeater (×4)158 before being spread by the Codeword Walsh Cover (W₁ ²) component159. The Repeater 158 repeats the two bits of the SRC symbol in series,four times, to produce an 8-bit codeword. For example, a two-bit SRCsymbol of ‘00’ is repeated by the Repeater 158 to produce a codeword of‘00000000.’ Similarly, a two-bit SRC symbol of ‘01’ is repeated by theRepeater 158 to produce a codeword of ‘01010101’.

The codewords produced by the Repeater 158 for all possible values ofthe two-bit SRC symbol are shown in Table 1 In essence, the Repeater 158implements a type of (8, 2) binary coding scheme in producing thecodewords. The minimum distance of the coding scheme shown in Table 1 is4 bits. As such, the coding scheme implemented in the Repeater 448provides a minimum distance of 4 bits.

TABLE 1 SRC Repetition Encoding SRC values Codeword 0x0 (00) 000000000x1 (01) 01010101 0x2 (10) 10101010 0x3 (11) 11111111

The (8, 2) repetition coding scheme described above may not be optimal,as determined by various measures. One such measure is the minimumdistance between codewords. The larger the minimum distance betweencodewords, the stronger the error correction capability. As such,embodiments of the present invention are directed to providing an (8, 2)code that provides a larger minimum distance (and therefore strongererror correction capability) relative to the (8, 2) repetition codedescribed with reference to FIG. 1 and Table 1. Particular embodimentsare directed to providing such an (8, 2) code for conveying up to 4distinct spatial rank values (e.g., for use in systems employing 4transmit antennas).

According to one embodiment, a maximal value of the minimum distance isachieved. With regard to determining this value for a given set ofcodes, the Plotkin bound will now be described. In general, for givenvalues of ‘n’ and ‘k’, the maximal minimum distance among all (n, k)codes may be difficult to determine However, within the realm of (8, 2)codes, the maximal value of the minimum distance can be determined bycalculating the Plotkin bound. The Plotkin bound describes therelationship between minimum distance, number of codewords and the bitlengths of codewords. The Plotkin bound is a well-understood techniqueand is described in, for example, a publication authored by John G.Proakis, “Wiley Encyclopedia of Telecommunications,” Wiley Interscience,N.J., 2003, vol. 2, pp 929-935.

Assuming a general binary [n, k, d] code where n is a number of bits ina codeword, k is a number of bits of information carried in thecodeword, and d is the minimum distance between codewords, then thePlotkin bound can be expressed as in Equations (1) below.

$\quad\left\{ {\begin{matrix}{2^{k} \leq {2\left( \frac{d}{{2d} - n} \right)}} & {{{{if}\mspace{14mu} d} = {even}},{d > \frac{n}{2}}} \\{2^{k} \leq {4\; d}} & {{{{if}\mspace{14mu} d} = {even}},{d = \frac{n}{2}}} \\{2^{k} \leq {2\left( \frac{d + 1}{{2d} + 1 - n} \right)}} & {{{{if}\mspace{14mu} d} = {odd}},{d > \frac{n - 1}{2}}} \\{2^{k} \leq {4\left( {d + 1} \right)}} & {{{{if}\mspace{14mu} d} = {odd}},{d = \frac{n - 1}{2}}}\end{matrix}\quad} \right.$

Alternatively, the Plotkin bound can be expressed as in Equations (2)below. Equations (2) more clearly express the limitations on the valueof the minimum distance.

$\quad\left\{ \begin{matrix}{d \leq {n \times \frac{2^{k - 1}}{2^{k} - 1}}} & {{{{if}\mspace{14mu} d} = {even}},{d > \frac{n}{2}}} \\{d = {\frac{n}{2} \geq 2^{k - 2}}} & {{{{if}\mspace{14mu} d} = {even}},{d = \frac{n}{2}}} \\{d \leq {{\left( {n - 1} \right) \times \frac{2^{k - 1}}{2^{k} - 1}} + \frac{1}{2^{k} - 1}}} & {{{{if}\mspace{14mu} d} = {odd}},{d > \frac{n - 1}{2}}} \\{d = {\frac{n - 1}{2} \geq {2^{k - 2} - 1}}} & {{{{if}\mspace{14mu} d} = {odd}},{d = \frac{n - 1}{2}}}\end{matrix} \right.$

Based on Equations (1) and (2), it is calculated that the maximalminimum distance among (8, 2) codes is 5 bits. Equation (3) belowillustrates the calculations for the case of (8, 2) codes.

$\begin{matrix}{{d \leq {{\left( {n - 1} \right) \times \frac{2^{k - 1}}{2^{k} - 1}} + \frac{1}{2^{k} - 1}}} = {{\left( {8 - 1} \right) \times \frac{2^{2 - 1}}{2^{2} - 1}} + \frac{1}{2^{2} - 1}}} \\{= {{7 \times \frac{2}{3}} + \frac{1}{3}}} \\{= \frac{15}{3}} \\{= 5}\end{matrix}$ ${{{if}\mspace{14mu} d} = {odd}},{d > \frac{n - 1}{2}}$

However, as previously described, the minimum distance of the codingscheme shown in Table 1 (and implemented in the Repeater 448 of FIG. 1)is only 4 bits. This minimum distance of 4 bits is less than the maximalminimum distance of 5 bits, as calculated using the Plotkin bound. Assuch, embodiments of the invention are directed towards designing and/orutilizing a coding scheme that provides improved performance relative tothe repetition encoding scheme of Table 1. In particular, exemplaryembodiments are directed to designing and/or utilizing an (8, 2) code,the codewords of which provide the maximal minimum distance of 5 bits.

Regarding error correction capability, if the minimum distance of agiven code is equal to or greater than (2a+1), where ‘a’ is an integer,then up to ‘a’ bit errors can be corrected. Under this formulation, inthe repetition encoding scheme of Table 1, the minimum distance is 4bits, and, therefore, up to 1 bit error can be corrected. In contrast,in a code that provides a minimum distance of 5 bits, up to 2 bit errorscan be corrected. This increase in the number of bit errors that can becorrected reflects a significant improvement relative to the repetitionencoding scheme of Table 1.

According to one embodiment, an (8, 2) code is designed using a simplexcode and a shortened Hamming code.

Belonging to the field of (n, 2) codes, in which the number ofinformation bits is two, is a (3, 2) simplex code. In general, simplexcodes may be described as (n, k) codes, where n is equal to 2k−1. Assuch, if the number of information bits is 2, then n=2(2)−1=3, and thecorresponding simplex code is a (3, 2) simplex code. Codewords of anexample of a (3, 2) simplex code are shown in Table 2 below.

TABLE 2 Example of (3, 2) Simplex code SRC values Codeword 0x0 (00) 0000x1 (01) 101 0x2 (10) 011 0x3 (11) 110

Simplex codes are optimal in the sense that they meet the upper bound ofthe Plotkin bound. For example, the (3, 2) simplex code shown above inTable 2 achieves the maximal minimum distance of 2. It should be notedthat, if the individual bits of the codewords are entered in the form ofa matrix (e.g., a 4×3 matrix), swapping entries of one matrix columnwith those of another matrix column (or swapping entries of one matrixrow with those of another matrix row) does not affect theminimum-distance aspect of the coding performance (i.e., the same codingperformance is provided). Also, changing the value of codeword bits from1 to 0 and from 0 to 1 also does not affect this aspect of the codingperformance.

In addition, changing the mapping between information values andcodewords also does not affect coding performance. For example, in theabove Table 2, the SRC value of 0×0 is mapped to the codeword “000” andthe SRC value of 0×1 is mapped to the codeword “101”. If the mappingwere changed such that the SRC value of 0×0 is mapped to the codeword“101” and the SRC value of 0×1 is mapped to the codeword “000”, thecoding performance would not be affected. Therefore, it is understoodthat Table 2 shows but one example of a (3, 2) simplex code and thatmultiple variations of this code may be suitable.

Also belonging to the field of (n, 2) codes, in which the number ofinformation bits is two, is the (5, 2) shortened Hamming code (5, 2).More details regarding the (5, 2) shortened Hamming code will bepresented below. However, selected general information regarding Hammingcodes will first be presented. In general, an [n, k, d] binary Hammingcode has properties as defined in Table 3 below.

TABLE 3 Properties of Hamming code Parameter Value Number of codewordbits n = 2^(m) − 1 Number of information bits k = 2^(m) − m − 1 Numberof parity bits n − k = m Minimum distance d = 3

One representative example of a Hamming code having a relatively shortlength is a (7, 4) Hamming code. Such a Hamming code may be shortenedsuch that the shortened Hamming code satisfies the properties as shownin Table 4 below.

TABLE 4 Properties of shortened Hamming code Parameter Value Number ofcodeword bits n = 2^(m) − l − 1 Number of information bits k = 2^(m) − m− l − 1 Number of parity bits n − k = m Minimum distance d ≧ 3

Based on the properties shown in Table 4, if it is assumed that l=2,then the (7, 4) Hamming code can be shortened to a (5, 2) shortenedHamming code. One example of a (5, 2) shortened Hamming code is shown inTable 5.

TABLE 5 Example of (5, 2) shortened Hamming code SRC values Codeword 0x0(00) 00000 0x1 (01) 01101 0x2 (10) 10011 0x3 (11) 11110

As shown in Table 4, the shortened Hamming code provides a minimumdistance of at least 3. The example (5, 2) shortened Hamming code ofTable 5 provides a minimum distance of 3. Similar to changes describedpreviously with respect to the (3, 2) simplex code of Table 2, certainchanges to the codewords of the (5, 2) shortened Hamming code of Table 5will not affect coding performance of the code. For example, if theindividual bits of the codewords are entered in the form of a matrix(e.g., a 4×5 matrix), swapping entries of one matrix column with thoseof another matrix column (or swapping entries of one matrix row withthose of another matrix row) does not affect the minimum-distance aspectof the coding performance (i.e., the same coding performance isprovided). Also, changing the value of codeword bits from 1 to 0 andfrom 0 to 1 also does not affect this aspect of the coding performance.

In addition, changing the mapping between information values andcodewords also does not affect coding performance. For example, in theabove Table 5, the SRC value of 0×0 is mapped to the codeword “00000”and the SRC value of 0×1 is mapped to the codeword “01101”. If themapping were changed such that the SRC value of 0×0 is mapped to thecodeword “01101” and the SRC value of 0×1 is mapped to the codeword“00000”, the coding performance would not be affected. Therefore, it isunderstood that Table 5 shows but one example of a (5, 2) shortenedHamming code and that multiple variations of this code may be suitable.

According to one embodiment, an (8, 2) code is designed using a (3, 2)simplex code (e.g., the (3, 2) simplex code of Table 2) and a (5, 2)shortened Hamming code (e.g., the (5, 2) shortened Hamming code of Table5).

According to a particular embodiment, the codewords of the (8, 2) codeare formed by combining (or joining) the codewords of the (3, 2) simplexcode with the codewords of the (5, 2) shortened Hamming code. Forexample, for the SRC value of 0×1, the codeword of the (8, 2) code isformed by combining the corresponding codeword of the (3, 2) simplexcode (i.e., “101”) and the corresponding codeword of the (5, 2)shortened Hamming code (i.e., “01101”) to form a combined codeword of“10101101”. That is, the codewords of the (8, 2) code are formed bypasting the two codes (i.e., the (3, 2) simplex code and the (5, 2)shortened Hamming code) side by side. For example, for the SRC value of0×2, the codeword of the (8, 2) code is formed by pasting thecorresponding codeword of the (3, 2) simplex code (i.e., “011”) and thecorresponding codeword of the (5, 2) shortened Hamming code (i.e.,“10011”) to form a combined codeword of “01110011”. The codewords of theresulting (8, 2) code are shown in Table 6.

TABLE 6 Example of (8, 2) code by combining (3, 2) simplex code and (5,2) shortened Hamming code SRC values Codeword 0x0 (00) 00000000 0x1 (01)10101101 0x2 (10) 01110011 0x3 (11) 11011110

Regarding the codewords of Table 6, it can be observed that the first 3bits (i.e., the most significant 3 bits) of each codeword originate fromthe codewords of Table 2 and that the last 5 bits (i.e., the leastsignificant 5 bits) of each codeword originate from the codewords ofTable 5. The (8, 2) code of Table 6 provides the optimal performance inthat its codewords provide the maximal minimum distance (among (8, 2)codes)—i.e., a distance of 5 bits.

As previously described with respect to the (3, 2) simplex code and the(5, 2) shortened Hamming code, many variations of these codes can bemade without negatively affecting coding performance. Similarly,multiple variations of the (8, 2) code of Table 6 can be made. Forexample, if the individual bits of the codewords are entered in the formof a matrix (e.g., a 4×8 matrix), swapping entries of one matrix columnwith those of another matrix column (or swapping entries of one matrixrow with those of another matrix row) does not affect theminimum-distance aspect of the coding performance (i.e., the same codingperformance is provided). Also, changing the value of codeword bits from1 to 0 and from 0 to 1 also does not affect this aspect of the codingperformance.

In addition, changing the mapping between information values andcodewords also does not affect coding performance. For example, in theabove Table 6, the SRC value of 0×0 is mapped to the codeword “00000000”and the SRC value of 0×1 is mapped to the codeword “10101101”. If themapping were changed such that the SRC value of 0×0 is mapped to thecodeword “10101101” and the SRC value of 0×1 is mapped to the codeword“00000000”, the coding performance would not be affected. Therefore, itis understood that Table 6 shows but one example of a (8, 2) code andthat multiple variations of this code may be suitable. Furthermore, the(3, 2) simplex code of Table 2 and/or the (5, 2) shortened Hamming codeof Table 5 could be modified (as described previously) and then combinedto form an (8, 2) code. As such, it is understood that, according toembodiments of the invention, multiple variations of the (8, 2) code ofTable 6 may be suitable.

According to one embodiment, one variation of the (8, 2) code of Table 6is the (8, 2) code of Table 7 shown below. Similar to the code of Table6, the code of Table 7 provides a maximum minimum distance of 5.Relative to the codewords of Table 6, the codewords of Table 7 areformed by performing column swap operations, as described previously.That is, the codewords of Table 7 are formed by effectively moving (orshifting) the fourth and fifth most significant bits of each codeword tothe two least significant bit positions.

TABLE 7 One example of a variation of the (8, 2) code of Table 6 SRCvalues Codeword 0x0 (00) 00000000 0x1 (01) 10110101 0x2 (10) 011011100x3 (11) 11011011

The (8, 2) code of Table 7 may also be described as being formed byrepeating the (3, 2) simplex code of Table 2 two times and then joiningthe resulting codeword with the two corresponding information bits. Forexample, regarding the SRC value of 0×1, the codeword “10110101” can bedescribed as being formed by repeating the corresponding codeword ofTable 2 (“101”) two times and then joining the resulting codeword(“101101”) with the two corresponding information bits (“01”).

According to another embodiment, another variation of the (8, 2) code ofTable 6 is shown in Table 8 below. This variation is formed by moving4^(th) and 5^(th) columns of codewords in Table 6 to the beginning.

Similar to the code of Table 6, the code of Table 8 provides a maximumminimum distance of 5.

TABLE 8 Another example of a variants from (8, 2) code of Table 6 SRCvalues Codeword 0x0 (00) 00000000 0x1 (01) 01101101 0x2 (10) 100110110x3 (11) 11110110

According to another embodiment, another variation of the code of Table6 is the coding scheme shown in Table 9 below. This variation is formedby two steps from Table 8. The first step is to cyclically shift columnsfrom 3^(rd) through 5^(th) down by one, which means to move the specificbits, 3rd to 5th column bits, to the next codeword located at next rowsin Table 8. And the second step is to cyclically shift down columns from6th through 8th by two, which corresponds to remap the 6th to 8th columnbits to the two rows down codeword in Table 8.

Regarding the code of Table 9, special efforts have been made in orderto make the number of ones between codewords distributed as fairly aspossible.

TABLE 9 One example of variants from (8, 2) code inTable 6 SRC valuesCodeword 0x0 (00) 00110011 0x1 (01) 01000110 0x2 (10) 10101000 0x3 (11)11011101

As described previously, it is understood that there are embodiments ofthe invention include variations of the (8, 2) code of Table 6. Examplesof such variations were shown in Tables 7, 8 and 9. For convenience ofdescription, additional variations of the (8, 2) code of Table 6 willnot be presented below.

According to one embodiment, an encoder in a transmitter of a mobilestation (MS) in a MIMO system is configured to encode information bits(e.g., information regarding spatial rank) in accordance with a codingscheme such as the scheme of Table 6 (or Table 7, Table 8, Table 9, or asuitable variation thereof.) An exemplary embodiment of such atransmitter will now be described with reference to FIG. 2.

With reference to FIG. 2, portions of an MS transmitter in a MIMO systemare configured to encode and modulate information including spatial rankand spatial signature. In the following description regarding FIG. 2,the spatial rank and spatial signature information will be describedwith reference to a system employing 4 transmit antennas. It isunderstood that, in a system employing only 2 transmit antennas, certainparameters may differ from the 4-transmit-antenna system. For example,relative to a system employing 4 transmit antennas, a system employingonly 2 transmit antennas may require a different number of bits toconvey spatial rank and spatial signature information.

With reference to FIG. 2, a transmitter (e.g., mobile communicationmodule 413 or controller 480 of FIG. 4) of the mobile terminal 40 isconfigured to encode and modulate a four-bit spatial signature and atwo-bit spatial rank for a system employing four transmit antennas.

The transmitter includes an In-Phase branch (I-Branch) 10 and aQuadrature Branch (Q-Branch) 15′. The I-Branch 10 includes aBi-Orthogonal Encoder 101, a Codeword Walsh Cover (W₀ ²) component 102,a Signal Point Mapper 103, a spatial signature channel (SSC) Gainelement 104, a Repeater (×8) 105, and a Modulator 106. The Q-Branch 15′includes a Bi-Orthogonal Encoder 151, a Codeword Walsh Cover (W₀ ²)component 152, a Signal Point Mapper 153, a direct rate control (DRC)Channel Gain element 154, Modulators 155 and 156, and a Walsh Cover(W_(i) ⁸) component 157. In addition, the Q-Branch 15′ includes anEncoder 168, a Codeword Walsh Cover (W₁ ²) component 159, a Signal PointMapper 160, a spatial rank channel (SRC) Gain element 161, a Repeater(×8) 162, and an adder 163.

With continued reference to FIG. 2, a four-bit SSC symbol is input tothe I-Branch 10. A two-bit SRC symbol and a four-bit DRC symbol areinput to the Q-Branch 15′. Because the SRC symbol is two bits long, thesymbol can convey up to 4 distinct spatial rank values (e.g., spatialrank values ranging from 0 to 3, ranging from 1 to 4, etc.). Similarly,because the SSC symbol is four bits long, it can support up to sixteendistinct spatial signatures. These spatial signatures may be predefinedfor the system, predefined for each particular sector, or negotiatedduring connection setup. According to various embodiments, a set ofdistinct spatial signatures numbering from 9 to 15 are predefined ornegotiated.

As previously described, the two-bit SRC symbol is input to the Q-Branch15′. In more detail, the two-bit SRC symbol is input to the Encoder 168before being spread by the Codeword Walsh Cover (W₁ ²) component 159.The Encoder 168 is configured to encode the two-bit SRC symbol inaccordance with a coding scheme such as the scheme of Table 6 (or Table7, Table 8, Table 9, or a suitable variation thereof) For example,according to a particular embodiment in which the Encoder 168 isconfigured to encode the two-bit SRC symbol in accordance with thecoding scheme of Table 6, a two-bit SRC symbol of ‘00’ is encoded by theEncoder 168 as a codeword of ‘00000000’. Similarly, a two-bit SRC symbolof ‘01’ is encoded by the Encoder 168 as a codeword of ‘10101101’.According to other embodiments, the Encoder 168 is configured to encodethe two-bit SRC symbol in accordance with a suitable variation of thecoding scheme of Table 6 (e.g., the coding scheme of Table 7, the codingscheme of Table 8, the coding scheme of Table 9, or some other suitablevariation of the Table 6 coding scheme, created, for example, bymodifying the Table 6 coding scheme, as described previously.)

In essence, the Encoder 168 implements an (8, 2) binary coding scheme inproducing the codewords. The minimum distance of the coding scheme is 5bits. As such, the coding scheme implemented in the Encoder 168 providesa minimum distance of 5 bits. Therefore, the coding scheme implementedin the Encoder 168 achieves the maximal minimum distance according tothe Plotkin bound.

The embodiment described with reference to FIG. 2 may be used in asystem employing 4 transmit antennas in HRPD revision C. The describedembodiment enhances the performance of feedback of spatial rankreporting. Unlike the system of FIG. 1, the embodiment of FIG. 2 employsencoder 168 rather than Repeater (×4) 158 to receive and encode theinput SRC symbol.

With reference to FIG. 1, the 2-bit rank information is repeated 4 timesin repeater 158 before length 2 Walsh code spreading in Codeword WalshCover (W₁ ²) component 159. Because the Walsh code spreading with length2 is common to both the SRC channel and the DRC, the replacement of therepeater 158 of FIG. 1 with the encoder 168 of FIG. 2 does not affectthe overall structure of these systems. As such, various aspects ofexisting channel structure and newly designed channels may be leftsignificantly unaltered.

With reference to FIG. 3, a method for transmitting feedback informationvia a Spatial Rank Index (SRI) channel will now be described. In box310, a value of a spatial rank index is determined at an access terminal(or mobile station). In box 320, feedback information indicating thedetermined value of the spatial rank index is transmitted, according toa prescribed coding. According to a particular embodiment, theprescribed coding corresponds to the coding scheme of Table 6.

FIG. 4 is a block diagram showing in more detail various componentswhich may be implemented in MS 40 according to various embodiments ofthe present invention. It is understood that greater or fewer componentsthan those shown may be implemented.

Referring to FIG. 4, the MS 40 (sometimes referred to herein as anaccess terminal or mobile terminal) may include a wireless communicationunit 410, an audio/video (A/V) input unit 420, a user input unit 430, asensing unit 440, an output unit 450, a memory 460, an interface unit470, a controller (or control unit) 480, and a power supply unit 490.Two or more of the wireless communication unit 410, the A/V input unit420, the user input unit 430, the sensing unit 440, the output unit 450,the memory 460, the interface unit 470, the controller 480, and thepower supply unit 490 may be incorporated into a single unit, or some ofthe wireless communication unit 410, the A/V input unit 420, the userinput unit 430, the sensing unit 440, the output unit 450, the memory460, the interface unit 470, the controller 480, and the power supplyunit 490 may be divided into two or more smaller units.

The wireless communication unit 410 may include a broadcast receptionmodule 411, a mobile communication module 413, a wireless Internetmodule 415, a short-range communication module 417, and a globalpositioning system (GPS) module 419.

The broadcast reception module 411 receives a broadcast signal and/orbroadcast-related information from an external broadcast managementserver through a broadcast channel. Examples of a broadcast channelinclude a satellite channel and a terrestrial channel. The broadcastmanagement server may be a server which generates broadcast signalsand/or broadcast-related information and transmits the generatedbroadcast signals and/or the generated broadcast-related information ormay be a server which receives and then transmits previously-generatedbroadcast signals and/or previously-generated broadcast-relatedinformation.

Examples of broadcast-related information include broadcast channelinformation, broadcast program information, and broadcast serviceprovider information. Examples of the broadcast signal include a TVbroadcast signal, a radio broadcast signal, a data broadcast signal, orthe combination of a data broadcast signal and either a TV broadcastsignal or a radio broadcast signal. The broadcast-related informationmay be provided to MS 40 through a mobile communication network. In thiscase, the broadcast-related information may be received by the mobilecommunication module 413, rather than by the broadcast reception module411. The broadcast-related information may come in various forms, forexample, electronic program guide (EPG) of digital multimediabroadcasting (DMB) or electronic service guide (ESG) of digital videobroadcast-handheld (DVB-H).

Broadcast reception module 411 may receive the broadcast signal usingvarious broadcasting systems such as digital multimediabroadcasting-terrestrial (DMB-T), digital multimediabroadcasting-satellite (DMB-S), media forward link only (MediaFLO),DVB-H, and integrated services digital broadcast-terrestrial (ISDB-T).In addition, the broadcast reception module 411 may be configured to besuitable for nearly all types of broadcasting systems other than thoseset forth herein.

The broadcast signal and/or the broadcast-related information receivedby the broadcast reception module 411 may be stored in memory 460.

The mobile communication module 413 transmits wireless signals to orreceives wireless signals from at least one or more of a base station,an external station, and a server through a mobile communicationnetwork. The wireless signals may include various types of dataaccording to whether the MS 40 transmits/receives voice call signals,video call signals, or text/multimedia messages.

The wireless Internet module 415 may be a module for wirelesslyaccessing the Internet. The wireless Internet module 415 may be embeddedin the MS 40 or may be installed in an external device.

The short-range communication module 417 may be a module for short-rangecommunication. The short-range communication module 417 may use variousshort-range communication techniques such as Bluetooth®, radio frequencyidentification (RFID), infrared data association (IrDA), ultra wideband(UWB), and ZigBee®.

The GPS module 419 may receive position information from one or moresatellites (e.g., GPS satellites).

The A/V input unit 420 may be used to receive audio signals or videosignals. The A/V input unit 420 may include one or more cameras 421 anda microphone 423. The camera 421 processes various image frames such asstill images or moving images captured by an image sensor during a videocall mode or an image capturing mode. The image frames processed by thecamera 421 may be displayed by a display module 451.

The image frames processed by the camera 421 may be stored in the memory460 or may be transmitted outside the MS 40 through the wirelesscommunication unit 410. The MS 40 may include more than two cameras.

The microphone 423 receives external sound signals during a call mode, arecording mode, or a voice recognition mode with the use of a microphoneand converts the sound signals into electrical sound data. In the callmode, the mobile communication module 413 may convert the electricalsound data into data that can be readily transmitted to a mobilecommunication base station and then output the data obtained by theconversion. The microphone 423 may use various noise removal algorithmsto remove noise that may be generated during the reception of externalsound signals.

The user input unit 430 generates key input data based on user input forcontrolling the operation of the MS 40. The user input unit 430 may beimplemented as a keypad, a dome switch, a touch pad (either staticpressure or constant electricity), a jog wheel, or a jog switch. Inparticular, if the user input unit 430 is implemented as a touch pad andforms a mutual layer structure along with the display module 451, theuser input unit 430 and the display module 451 may be collectivelyreferred to as a touch screen.

The sensing unit 440 determines a current state of the MS 40 such aswhether the MS 40 is opened or closed, the position of the MS 40 andwhether the MS 40 is placed in contact with a user. In addition, thesensing unit 440 generates a sensing signal for controlling theoperation of the MS 40.

For example, when the MS 40 is a slider-type mobile phone, the sensingunit 440 may determine whether the MS 40 is opened or closed. Inaddition, the sensing unit 440 may determine whether the MS 40 ispowered by the power supply unit 490 and whether the interface unit 470is connected to an external device.

The sensing unit 440 may include an acceleration sensor 443.Acceleration sensors are a type of device for converting an accelerationvariation into an electric signal. With recent developments inmicro-electromechanical system (MEMS) technology, acceleration sensorshave been widely used in various products for various purposes. Forexample, an acceleration sensor may be used as an input device for acomputer game and may sense the motion of the human hand during acomputer game.

Two or three acceleration sensors 443 representing different axialdirections may be installed in the MS 40. Alternatively, only oneacceleration sensor 443 representing a Z axis may be installed in the MS40.

The output unit 450 may output audio signals, video signals, and alarmsignals. The output unit 450 may include the display module 451, anaudio output module 453, and an alarm module 455.

The display module 451 may display various information processed by theMS 40. For example, if the MS 40 is in a call mode, the display module451 may display a user interface (UI) or a graphical user interface(GUI) for making or receiving a call. If the MS 40 is in a video callmode or an image capturing mode, the display module 451 may display a UIor a GUI for capturing or receiving images.

If the display module 451 and the user input unit 430 form a mutuallayer structure and are thus implemented as a touch screen, the displaymodule 451 may be used not only as an output device but also as an inputdevice. If the display module 451 is implemented as a touch screen, thedisplay module 451 may also include a touch screen panel and a touchscreen panel controller.

The touch screen panel is a transparent panel attached onto the exteriorof the MS 40 and may be connected to an internal bus of the MS 40. Thetouch screen panel monitors whether the touch screen panel is touched bya user. Once a touch input to the touch screen panel is detected, thetouch screen panel transmits a number of signals corresponding to thetouch input to the touch screen panel controller.

The touch screen panel controller processes the signals transmitted bythe touch screen panel and transmits the processed signals to thecontrol unit 480. The control unit 480 then determines whether a touchinput has been generated and which part of the touch screen panel hasbeen touched based on the processed signals transmitted by the touchscreen panel controller.

As described above, if the display module 451 and the user input unit430 form a mutual layer structure and are thus implemented as a touchscreen, the display module 451 may be used not only as an output devicebut also as an input device. The display module 451 may include at leastone of a liquid crystal display (LCD), a thin film transistor (TFT)-LCD,an organic light-emitting diode (OLED), a flexible display, and athree-dimensional (3D) display.

The MS 40 may include two or more display modules 451. For example, theMS 40 may include an external display module and an internal displaymodule.

The audio output module 453 may output audio data received by thewireless communication unit 410 during a call reception mode, a callmode, a recording mode, a voice recognition mode, or a broadcastreception mode or may output audio data present in the memory 460. Inaddition, the audio output module 453 may output various sound signalsassociated with the functions of the MS 40 such as receiving a call or amessage. The audio output module 453 may include a speaker and a buzzer.

The alarm module 455 may output an alarm signal indicating theoccurrence of an event in the MS 40. Examples of the event includereceiving a call signal, receiving a message, and receiving a keysignal. Examples of the alarm signal output by the alarm module 455include an audio signal, a video signal, and a vibration signal.

The alarm module 455 may output a vibration signal upon receiving a callsignal or a message. In addition, the alarm module 455 may receive a keysignal and may output a vibration signal as feedback to the key signal.

Once a vibration signal is output by the alarm module 455, the user mayrecognize that an event has occurred. A signal for notifying the user ofthe occurrence of an event may be output by the display module 451 orthe audio output module 453.

The memory 460 may store various programs necessary for the operation ofthe controller 480. In addition, the memory 460 may temporarily storevarious data such as a phonebook, messages, still images, or movingimages.

The memory 460 may include at least one of a flash memory type storagemedium, a hard disk type storage medium, a multimedia card micro typestorage medium, a card type memory (e.g., a secure digital (SD) orextreme digital (XD) memory), a random access memory (RAM), and aread-only memory (ROM). The MS 40 may operate a web storage, whichperforms the functions of the memory 460 on the Internet.

The interface unit 470 may interface with an external device that can beconnected to the MS 40. The interface unit 470 may be a wired/wirelessheadset, an external battery charger, a wired/wireless data port, a cardsocket such as for a memory card or a subscriber identification module(SIM)/user identity module (UIM) card, an audio input/output (I/O)terminal, a video I/O terminal, or an earphone.

The interface unit 470 may receive data from an external device or maybe powered by an external device. The interface unit 470 may transmitdata provided by an external device to other components in the MS 40 ormay transmit data provided by other components in the MS 40 to anexternal device.

The controller 480 may control the general operation of the MS 40. Forexample, the controller 480 may perform various control operationsregarding making/receiving a voice call, transmitting/receiving data, ormaking/receiving a video call.

The controller 480 may include a multimedia play module 481, which playsmultimedia data. The multimedia play module 481 may be implemented as ahardware device and may be installed in the controller 480.Alternatively, the multimedia play module 481 may be implemented as asoftware program.

The power supply unit 490 is supplied with power by an external powersource or an internal power source and supplies power to othercomponents in the MS 40.

In alternative implementations, certain logic operations may beperformed in a different order, modified or removed and still implementexemplary embodiments of the present invention. Moreover, operations maybe added to the above described logic and still conform to assortedimplementations of the invention.

Furthermore, the described embodiments may be implemented as a method,apparatus or article of manufacture using standard programming and/orengineering techniques to produce software, firmware, hardware, or anycombination thereof. The term “article of manufacture” as used hereinrefers to code or logic implemented in hardware logic (e.g., anintegrated circuit chip, Field Programmable Gate Array (FPGA),Application Specific Integrated Circuit (ASIC), etc.) or a computerreadable medium (e.g., magnetic storage medium (e.g., hard disk drives,floppy disks, tape, etc.), optical storage (CD-ROMs, optical disks,etc.), volatile and non-volatile memory devices (e.g., EEPROMs, ROMs,PROMs, RAMs, DRAMs, SRAMs, firmware, programmable logic, etc.). Code inthe computer readable medium is accessed and executed by a processor.

The code in which exemplary embodiments are implemented may further beaccessible through a transmission media or from a file server over anetwork. In such cases, the article of manufacture in which the code isimplemented may include a transmission media, such as a networktransmission line, wireless transmission media, signals propagatingthrough space, radio waves, infrared signals, etc. Of course, thoseskilled in the art will recognize that many modifications may be made tothis configuration, and that the article of manufacture may comprise anyinformation bearing medium known in the art.

The logic implementation shown in the figures describe specificoperations as occurring in a particular order. In alternativeimplementations, certain logic operations may be performed in adifferent order, modified or removed and still implement certainembodiments of the present invention. Moreover, operations may be addedto the above described logic and still conform to the describedimplementations.

The foregoing embodiments and features are merely exemplary and are notto be construed as limiting the present invention. The present teachingscan be readily applied to other types of apparatuses and processes. Thedescription of such embodiments is intended to be illustrative, and notto limit the scope of the claims. Many alternatives, modifications, andvariations will be apparent to those skilled in the art.

1. A method for transmitting feedback information via a Spatial RankIndex (SRI) channel, the method comprising: determining, at an accessterminal, a value of a spatial rank index; transmitting, from the accessterminal through the SRI channel, feedback information indicating thedetermined value of the spatial rank index according to a prescribedcoding, wherein a codeword of the prescribed coding is one of:(0,0,0,0,0,0,0,0), (1,0,1,0,1,1,0,1), (0,1,1,1,0,0,1,1), or(1,1,0,1,1,1,1,0).
 2. The method of claim 1, wherein the prescribedcoding is configured to provide a minimum distance of
 5. 3. The methodof claim 1, wherein the codeword is: (0,0,0,0,0,0,0,0) when thedetermined value of the spatial rank index is 1, (1,0,1,0,1,1,0,1) whenthe determined value of the spatial rank index is 2, (0,1,1,1,0,0,1,1)when the determined value of the spatial rank index is 3, and(1,1,0,1,1,1,1,0) when the determined value of the spatial rank index is4.
 4. A method for generating/transmitting a codeword, the methodcomprising: determining, at an access terminal, information regarding avalue of a spatial rank; and generating, at the access terminal, thecodeword to represent the determined information, the generatingcomprising combining a first codeword of a (3, 2) simplex code and asecond codeword of a (5, 2) shortened Hamming code.
 5. The method ofclaim 4, wherein the codeword is one of: (0,0,0,0,0,0,0,0),(1,0,1,0,1,1,0,1), (0,1,1,1,0,0,1,1), or (1,1,0,1,1,1,1,0).
 6. Themethod of claim 4, wherein the first codeword of the (3,2) simplex codeis one of: (0,0,0), (1,0,1), (0,1,1), or (1,1,0); and wherein the secondcodeword of the (5,2) shortened Hamming code is one of: (0,0,0,0,0),(0,1,1,0,1), (1,0,0,1,1), or (1,1,1,1,0).
 7. The method of claim 4,wherein the value of the spatial rank is regarding a number of speciallayers requested by the access terminal for use by an access network. 8.The method of claim 4, wherein the codeword is: (0,0,0,0,0,0,0,0) whenthe value of the spatial rank is 1, (1,0,1,0,1,1,0,1) when the value ofthe spatial rank is 2, (0,1,1,1,0,0,1,1) when the value of the spatialrank is 3, and (1,1,0,1,1,1,1,0) when the value of the spatial rank is4.
 9. An access terminal for transmitting feedback information via aSpatial Rank Index (SRI) channel, the access terminal comprising: acontroller configured to determine a value of a spatial rank index; atransmitter configured to transmit feedback information via the SRIchannel, wherein the feedback information indicates the determined valueof the spatial rank index according to a prescribed coding, and whereina codeword of the prescribed coding is one of: (0,0,0,0,0,0,0,0),(1,0,1,0,1,1,0,1), (0,1,1,1,0,0,1,1), or (1,1,0,1,1,1,1,0).
 10. Theaccess terminal of claim 9, wherein the prescribed coding is configuredto provide a minimum distance of
 5. 11. The access terminal of claim 9,wherein the codeword is: (0,0,0,0,0,0,0,0) when the determined value ofthe spatial rank index is 1, (1,0,1,0,1,1,0,1) when the determined valueof the spatial rank index is 2, (0,1,1,1,0,0,1,1) when the determinedvalue of the spatial rank index is 3, and (1,1,0,1,1,1,1,0) when thedetermined value of the spatial rank index is 4.